This invention relates to a multiple function driver circuit, in particular one for driving four light emitting diodes and one piezo horn.
In many electronic systems incorporating integrated circuits, the component that is usually the largest contributor to total system manufacturing cost is the integrated circuit itself. The cost of an integrated circuit is based upon several factors including the number of leads and size of the IC plastic assembly. For example, an 8 pin package is less costly than a pin package.
FIG. 1 is a representation of a multiple function circuit of the prior art. In particular, an electronic warning alarm system which selectively flashes light emitting diodes (LEDs) and activates an audible warning transducer (Piezo horn) depending upon the requirements of the control circuit is shown. Additionally, this circuit permits the piezo horn to be converted to a sound to voltage transducer so that it can listen as a microphone to external sounds. Such a system may be useful in applications such as an automobile where the horn may be used as a microphone to listen to the engine while the LEDs are used to indicate diagnoses of problems within the automobile. The prior art circuit includes one transistor for each LED. To turn an LED on, its respective transistor is switched on. Thus, there is a terminal for each one of the four LED drivers. A fifth terminal is provided for operating a piezo horn. The fifth terminal is connected between two transistors which can alternately turn on and off to cause the horn to sound. When both the transistors connected to the fifth terminal are off, the piezo horn can be used as a microphone. Thus, for operating four LEDs and one piezo horn, the prior art circuit required five terminals or five pins on an integrated circuit. The integrated circuit will also require a pin for ground and a control voltage. If two more pins are required for other functions on the control circuit, an eight pin package cannot be used, thus raising the cost of such an integrated circuit.
It is an objective of the present invention to minimize the number of pins required to operate four LEDs and a piezo horn.